PZT-based piezoelectric ceramics containing Pb(Ti, Zr)O3 (hereinafter referred to as “PZT”) as a major component are widely known as typical piezoelectric ceramics used for multilayer piezoelectric devices, such as piezoelectric actuators, piezoelectric resonators, and piezoelectric filters.
Furthermore, as multilayer piezoelectric devices including PZT-based piezoelectric ceramics, devices which are fabricated by alternately stacking internal electrode layers composed of an Ag—Pd alloy and ceramic layers composed of a PZT-based piezoelectric ceramic, followed by simultaneous firing, are often used. However, since Pd is expensive, research and development has been actively carried out on multilayer piezoelectric devices in which inexpensive Cu is used as the material for internal electrodes.
For example, Patent Document 1 describes a multilayer piezoelectric device including internal electrode layers containing Cu as a major component, and a PZT-based piezoelectric ceramic.
Patent Document 1 discloses a multilayer piezoelectric device including electrodes containing Cu as a major component, and a piezoelectric ceramic, in which the piezoelectric ceramic contains, as a major component, a perovskite oxide represented by general formula ABO3, the A site including Pb, the B site including Zr and Ti, wherein the B site includes an acceptor element which is a divalent metal element and a donor element which is a pentavalent metal element, and the relationship 0.42<a/b<0.5 is satisfied, wherein a represents the total molar amount of the acceptor element, and b represents the total molar amount of the donor element.
When the electrodes containing Cu as the major component and the piezoelectric ceramic are simultaneously fired, Cu in the electrodes diffuses into the piezoelectric ceramic and acts as a divalent acceptor element in the state of Cu2+. Consequently, in the multilayer piezoelectric device of Patent Document 1, in the B site of the piezoelectric ceramic composition, the donor content is adjusted to be in excess so that the relationship 0.42<a/b<0.5 is satisfied, wherein a represents the total molar amount of the acceptor element, and b represents the total molar amount of the donor element. Thereby, the decrease in the average valence in the B site due to the diffusion of Cu is cancelled out, enabling prevention of a decrease in the piezoelectric constant.
Patent Document 1: International Publication No. WO2005/071769 pamphlet